ABSTRACTA highly efficient process of synthesizing a cardanol‐bonded cellulose thermoplastic has been developed by using isocyanate‐modified cardanol. As recently shown by us, the thermoplastic consisting of cellulose diacetate (CDA) and cardanol extracted from cashew nutshells performed high practical properties such as bending strength, heat resistance and water resistance. However, its synthesis process by esterification using acid chlorides of cardanol in a solvent as a common procedure, required high energy consumption by using a large amount of poor solvent to isolate the resulting product from the solvent. Using an isocyanate‐modified cardanol, 3‐pentadecylcyclohexyl (6‐isocyanatohexyl) carbamate (PICC) greatly improved the productivity of the modified cardanol‐bonded CDA (PICC‐bonded CDA). After bonding PICC to CDA in a solvent, the remaining PICC coagulated and was easily removed by filtration, which resulted in remarkably simplifying the separation process of the product. The resulting PICC‐bonded CDA showed insufficient thermoplasticity due to its high interaction between PICC parts. Additional bonding propionyl group improved the thermoplasticity while maintaining good thermal and mechanical properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1578–1587, 2013